Swar bars for autocrossing a road car? (1969 510)

[slowlearner]

Having done my first tarmac autocross on Saturday, it occurred to me the car is rolling around and unloading the rear wheels a bit more than it should. Front feels very planted, but the rear not so much. Vid below shows my quickest efforts.

 

 

Looking from some advice.

 

Current setup...

 

Front; Factory 810 (200b) front struts and springs with Bilstein inserts, stock sway bar (1969).

Rear; Kings rally spec springs, Bilstein shocks, no sway bar.

Diff; Subaru STi R180 2 way plate LSD with Datsun output shafts.

 

I don't want to lower the car more, or make it harder. It has reasonable road manners and will always be a road car first. Yes, better tyres will help too. Already thinking about that.

 

So thoughts? Sway bars? Rear? Diameter?

 

Edited March 11, 2025 by slowlearner

[banzai510(hainz)]

ask  or pm icehouse on here. he is good on this one. You want maybe no sway bar depending on track setup

[ggzilla]

as a general rule of thumb, a rear anti-sway bar will unload the inside tire more. So proceed with caution. You might need to modify the front rates to get it to balance better. E.g. going from the stock ~90 lbs springs on the front to 200, maybe 175 would be better balance and a slightly more comfortable ride at the same time? Many would say get stiffer springs for the rear. King springs (at least from what I've seen) are not super stiff, so that may be an issue

[Rustbin]

When I got my 510 it had a 1 inch front bar and the car cornered very flat but it also had a rear bar that had been disconnected on one end, I reconnected the rear  bar and the cornering suffered a little. That convinced me to remove the rear bar after that. I would recommend going with a thicker front bar first. Mind you I'm wasn't racing just driving too fast on winding roads. 

[datzenmike]

All vehicles have a very small amount of under steer built in. It's the easiest to control and get out of, just lift the gas and put brake on. Adding a rear sway bar or increasing the thickness of one tends to increase away from under steer and enter over steer.  To compensate I believe you increasing the front bar stiffness. There are many many causes and corrections for under/over steer.

[slowlearner]

On 3/12/2025 at 10:44 AM, ggzilla said:

as a general rule of thumb, a rear anti-sway bar will unload the inside tire more. So proceed with caution. You might need to modify the front rates to get it to balance better. E.g. going from the stock ~90 lbs springs on the front to 200, maybe 175 would be better balance and a slightly more comfortable ride at the same time? Many would say get stiffer springs for the rear. King springs (at least from what I've seen) are not super stiff, so that may be an issue

 

I think the rear springs are reasonably stiff. Certainly stiffer than the aftermarket spring I got it with, that I'm certain were already stiffer than stock.

 

@datzenmike I didn't feel the car understeering at all. There was only a little oversteer when the car got unsettled or under max power (which isn't a lot, LOL). I'm just concerned about the amount of body roll. I could fit better tyres too, but I was thinking one thing at a time.

[datzenmike]

What i meant was it moves the car towards under steer. You may have an abundance of over steer or other factors and it didn't have much of an effect.

[Pounding Rox Truck Shop]

A slightly softer spring in the rear will help, or a welded diff. I ran into this autoxing my D21 hardbody. I have a Hellwig rear bar. To help with inner tire lifting I pulled the overload leaves. This made the rear a bit more compliant. Not perfect but more compliant.

Edited March 14, 2025 by Pounding Rox Truck Shop

[fiveoneO]

Most people seem to prefer not having a rear sway bar on a 510, but I actually like it. I run 200lb springs front and rear with a 1in front bar and a 3/4in rear bar. With the relatively light springs I run, I was getting more body roll than I wanted, going with larger sway bars definitely helped with that. I don't autocross or anything like that, I just enjoy a spirited drive from time to time. If you want to be more competitive, you'll probably need stiffer springs. Something to think about with sway bars, they do help with body roll, but they also reduce traction, especially if you don't get the balance quite right from front to rear.

[Z23T]

There is a good article over at the 510 Realm about suspension setups. It can be a bitch to get the website to load, keep trying and you'll eventually get in.

 

Here's the link. https://www.the510realm.com/viewtopic.php?t=1067